Converting many 'if else' statements to a cleaner approach [duplicate]

My code here detects if the mimeType is equals to some MIME type, if it is, it will do a certain conversion

public void convertToMp3(File src, File target,String mimeType){
    if(mimeType.equals("audio/mpeg")){
        ...
    }else if(mimeType.equals("audio/wav")){
        mp3ToWav();
    }else if(mimeType.equals("audio/ogg")){
        ...
    }else if(...){
    ... //More if and else here
}

I have shortened my code, because it has a lot of else if statements, What design pattern is suitable for removing many if and else or else if statements?

Solution 1:

You could have a Converter interface. Then you could create a class for each Mimetype like:

public interface Converter {

    public void convertToMp3();
    public void convertToOgg();

}

public class MpegConverter implements Converter {

    public void convertToMp3() {
        //Code here
    }

    public void convertToOgg() {
        //Code here
    }

}

You would need a class like this for each converter. Then you could set up a map like this:

Map<String, Converter> mimeTypeMap = new HashMap<String, Converter>();

mimeTypeMap.put("audio/mpeg", new MpegConverter());

Then your convertToMp3 method becomes like this:

Converter converter = mimeTypeMap.get(mimeType);
converter.convertToMp3();

Using this approach you could easily add different converters in the future.

All untested, probably doesn't compile, but you get the idea

Solution 2:

If you use pre-JDK7, you may add an enum for all MIME types:

  public static enum MimeTypes {
      MP3, WAV, OGG
  }

  public class Stuff {
      ...
      switch (MimeTypes.valueOf(mimeType)) {
          case MP3: handleMP3(); break;
          case WAV: handleWAV(); break;
          case OGG: handleOGG(); break;
      }
  }

And have a look at the Stack Overflow question Java - Convert String to enum on how to convert Strings to enums.

Solution 3:

Consider using the Strategy design pattern and a Map to dispatch to the appropriate strategy. Particularly useful if you you will need additional functionality, in addition to a conversion for a particular mimeType, or the convertors are large and complicated code and you would want to place each convertor in its own .java file.

 interface Convertor {
    void convert(File src, File target);
 }

 private static void convertWav(File src, File target) {
    ...
 }

 ...

 private static final Map< String, Convertor > convertors = new ...;
 static {
    convertors.put("audio/wav", new Convertor {
       void convert(File src, File target) {
          convertWav(src, target);
       }
    });
    convertors.put("audio/ogg", new Convertor {
       void convert(File src, File target) {
          convertOgg(src, target);
       }
    });
    ...
 }

 public void convertToMp3(File src, File target, String mimeType){
     final Convertor convertor = convertors.get(mimeType);
     if (convertor == null ) {
        ...
     } else {
        convertor.convert(src, target);
     }
 }

Solution 4:

If you run the same methods for each case you should check State pattern